Neural circuitry involving the amygdala and hippocampus is thought to underlie anxiety (Rosen & Schulkin, 1998). When confronted with unpleasant and potentially harmful stimuli such as foul odors or tastes, PET-scans show increased bloodflow in the amygdala (Zald & Pardo, 1997; Zald, Hagen & Pardo, 2002). In these studies, the participants also reported moderate anxiety. This might indicate that anxiety is a protective mechanism designed to prevent the organism from engaging in potentially harmful behaviors.